Re: [PATCH v3 2/2] mm/mprotect: special-case small folios when applying write permissions

[Vlastimil Babka (SUSE)]

On 4/2/26 16:16, Pedro Falcato wrote:
> The common order-0 case is important enough to want its own branch, and
> avoids the hairy, large loop logic that the CPU does not seem to handle
> particularly well.
> 
> While at it, encourage the compiler to inline batch PTE logic and resolve
> constant branches by adding __always_inline strategically.
> 
> Suggested-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
> Tested-by: Luke Yang <luyang@xxxxxxxxxx>
> Signed-off-by: Pedro Falcato <pfalcato@xxxxxxx>

Can't say I'm thrilled about these hacks, but seems to work, so

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>


> +			if (likely(nr_ptes == 1)) {
> +				change_present_ptes(tlb, vma, addr, pte, 1,
> +					end, newprot, folio, page, cp_flags);
> +			} else {
> +				change_present_ptes(tlb, vma, addr, pte,
> +					nr_ptes, end, newprot, folio, page,
> +					cp_flags);
> +			}

I wonder if there's anything about this trick that ensures the compilers
will not eventually stop compiling it the way you intend. Have you talked to
compiler people? :)

> +
>  			pages += nr_ptes;
>  		} else if (pte_none(oldpte)) {
>  			/*